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在类的成员变量(全局变量)中,DateTime的默认值为: 0001-1-1 0:00:00
注:局部变量必须赋值才能使用
继承于System.ValueType的全是值（Struct）类型的:
System.ArgIterator
System.Boolean
System.Byte
System.Char
System.Collections.DictionaryEntry
System.Collections.Specialized.BitVector32
System.Collections.Specialized.BitVector32.Section
System.Configuration.Assemblies.AssemblyHash
System.Data.OracleClient.OracleBinary
System.Data.OracleClient.OracleBoolean
System.Data.OracleClient.OracleDateTime
System.Data.OracleClient.OracleMonthSpan
System.Data.OracleClient.OracleNumber
System.Data.OracleClient.OracleString
System.Data.OracleClient.OracleTimeSpan
System.Data.SqlTypes.SqlBinary
System.Data.SqlTypes.SqlBoolean
System.Data.SqlTypes.SqlByte
System.Data.SqlTypes.SqlDateTime
System.Data.SqlTypes.SqlDecimal
System.Data.SqlTypes.SqlDouble
System.Data.SqlTypes.SqlGuid
System.Data.SqlTypes.SqlInt16
System.Data.SqlTypes.SqlInt32
System.Data.SqlTypes.SqlInt64
System.Data.SqlTypes.SqlMoney
System.Data.SqlTypes.SqlSingle
System.Data.SqlTypes.SqlString
System.DateTime
System.Decimal
System.Diagnostics.CounterSample
System.Diagnostics.SymbolStore.SymbolToken
System.Double
System.Drawing.CharacterRange
System.Drawing.Color
System.Drawing.Point
System.Drawing.PointF
System.Drawing.Rectangle
System.Drawing.RectangleF
System.Drawing.Size
System.Drawing.SizeF
System.EnterpriseServices.BOID
System.EnterpriseServices.XACTTRANSINFO
System.Enum
System.Guid
System.Int16
System.Int32
System.Int64
System.IntPtr
System.IO.WaitForChangedResult
System.Reflection.Emit.EventToken
System.Reflection.Emit.FieldToken
System.Reflection.Emit.Label
System.Reflection.Emit.MethodToken
System.Reflection.Emit.OpCode
System.Reflection.Emit.ParameterToken
System.Reflection.Emit.PropertyToken
System.Reflection.Emit.SignatureToken
System.Reflection.Emit.StringToken
System.Reflection.Emit.TypeToken
System.Reflection.InterfaceMapping
System.Reflection.ParameterModifier
System.Runtime.InteropServices.ArrayWithOffset
System.Runtime.InteropServices.BIND_OPTS
System.Runtime.InteropServices.BINDPTR
System.Runtime.InteropServices.CONNECTDATA
System.Runtime.InteropServices.DISPPARAMS
System.Runtime.InteropServices.ELEMDESC
System.Runtime.InteropServices.ELEMDESC.DESCUNION
System.Runtime.InteropServices.EXCEPINFO
System.Runtime.InteropServices.FILETIME
System.Runtime.InteropServices.FUNCDESC
System.Runtime.InteropServices.GCHandle
System.Runtime.InteropServices.HandleRef
System.Runtime.InteropServices.IDLDESC
System.Runtime.InteropServices.PARAMDESC
System.Runtime.InteropServices.STATSTG
System.Runtime.InteropServices.TYPEATTR
System.Runtime.InteropServices.TYPEDESC
System.Runtime.InteropServices.TYPELIBATTR
System.Runtime.InteropServices.VARDESC
System.Runtime.InteropServices.VARDESC.DESCUNION
System.Runtime.Serialization.SerializationEntry
System.Runtime.Serialization.StreamingContext
System.RuntimeArgumentHandle
System.RuntimeFieldHandle
System.RuntimeMethodHandle
System.RuntimeTypeHandle
System.SByte
System.Security.Cryptography.DSAParameters
System.Security.Cryptography.RSAParameters
System.Single
System.Threading.LockCookie
System.Threading.NativeOverlapped
System.TimeSpan
System.TypedReference
System.UInt16
System.UInt32
System.UInt64
System.UIntPtr
System.Void
System.Web.UI.WebControls.FontUnit
System.Web.UI.WebControls.Unit
System.Windows.Forms.BindingMemberInfo
System.Windows.Forms.DataGridCell
System.Windows.Forms.LinkArea
System.Windows.Forms.Message
在我的一个程序里遇到这样一个问题？
在数据库中的某个字段类型为 datetime
页面上对应该字段的为一个text文本输入框，意思是输入时间。
string strId =txtId.Text.Trim();
string strName=txtName.Text.Trim();
string strPwd=txtPwd.Text.Trim();
string strExpiry=txtTime.Text.Trim(); //时间
System.Data.SqlClient.SqlParameter []parmCustomers = new SqlParameter[3];
parmCustomers[0] = new SqlParameter( "@C_Id", strId );
parmCustomers[1] = new SqlParameter( "@Name", strName );
parmCustomers[2] = new SqlParameter( "@Pwd", strPwd );
parmCustomers[3] = new SqlParameter("@Date",strExpiry);//如果现文本里没有输入时间
SqlServerDatabase obj = new SqlServerDatabase();
if ( obj.RunProc( "proc_AddUser", parmCustomers ) == 1 ) // 添加成功
{
Response.Write("<script type='text/javascript'>alert('Add Success！')</script>");
}
上段程序当然可以添加成功，
问题是当txtTime.Text什么都没输入的时候，数据库中的这个字段仍然会存储 1900-01-01 00:00:00.000
于是我就在parmCustomers[3] = new SqlParameter("@Date", " " )写入空字符串 或是 null ，可问题插入后数据库里还是显示1900-01-01
以下是解决办法：
于是加了判断： //注 数据库里时间字段要设置永许为空
string strExpiry=this.txtTime.Text.Trim();
System.Data.SqlClient.SqlParameter []parmCustomers = new SqlParameter[3];
parmCustomers[0] = new SqlParameter( "@C_Id", strId );
parmCustomers[1] = new SqlParameter( "@Name", strName );
parmCustomers[2] = new SqlParameter( "@Pwd", strPwd );
if(strExpiry.ToString()=="")
{
parmCustomers[3] = new SqlParameter("@Date",DBNull.Value);//如果文本框的时间为空的话就吧 strExpiry 改为 DBNull.Value 就OK了
}
else
{
parmCustomers[3] = new SqlParameter("@Date",strExpiry);//有值时
}
SqlServerDatabase obj = new SqlServerDatabase();
if ( obj.RunProc( "proc_AddUser", parmCustomers ) == 1 ) // 添加成功
{
Response.Write("<script type='text/javascript'>alert('Add Success！')</script>");
}
如果是Sql语句直接插入的话
insert into AddUser （name，pwd）values（'test'，'123'）
date字段 就不要写入到插入的Ｓｑｌ语句里 这样数据库里的值就为空了。。。
-------------------------------------无敌分割线-----------------------------------------
DateTime是结构体，他不能直接被赋值成 null， 我建议是赋值成以下的方法
DateTime s = default( DateTime );
或是
DateTime s = DateTime.MinValue;
或是
DateTime s=DateTime.MaxValue; //DateTime最大值为:9999-12-31 23:59:59
比较的时候直接if(s == DateTime.MinValue;)// 到了显示的时候，判断一下，如果是s == DateTime.MinValue 就可以在数据库传参的时候赋值为DBNull.value
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